The present invention relates to a semiconductor device including a plurality of semiconductor elements stacked to each other and a method of fabricating the semiconductor device, and particularly to a technique capable of stacking semiconductor elements to each other without any limitation by outer sizes of the semiconductor elements.
If one semiconductor element is mounted on a wiring board, then an area of the wiring board is occupied with the semiconductor device, and thereby another semiconductor element is no longer mounted on the wiring board. On the other hand, in recent years, electronic devices such as video cameras, CDs, and cellular phones have been required to be further reduced in size and further enhanced in performance. To meet such a requirement, there has been proposed a semiconductor device, in which a semiconductor element mounting area becomes twice that of a prior art semiconductor device although the semiconductor device uses the same wiring board as that used for the related art semiconductor device.
For example, a related art semiconductor device 1 shown in FIG. 4 includes two semiconductor elements 3 and 5, wherein a surface (back surface) 9 opposed to an electric connection surface 7 of the semiconductor element 3 is superimposed to a surface (back surface) 13 opposed to an electric connection surface 11 of the other semiconductor element 5 and is bonded thereto by means of adhesive 15, and the electric connection surface 11 of the upper semiconductor element 5 is electrically connected to segments of wiring on a wiring board 19 by means of bonding wires 17 while the electric connection surface 7 of the lower semiconductor element 3 is electrically connected to segments of the wiring on the wiring board 19 by means of bumps 23.
Another related art semiconductor device 25 shown in FIG. 5 includes two semiconductor elements 27 and 29, in which a surface (back surface) 33 opposed to an electric connection surface 31 of the semiconductor element 27 is die-bonded to a wiring board 19 by means of adhesive 15 and electrodes of the semiconductor element 27 are electrically connected to segments of wiring on the wiring board 19 by means of bonding wires 17, and the other semiconductor element 29 is bonded, in a flip-chip bonding manner, to a front surface of the semiconductor element 27 by means of bumps 35.
With each of the semiconductor devices 1 and 25, a mounting density of the semiconductor device becomes twice that of a conventional semiconductor device in which a mounting area is occupied with one semiconductor element. Accordingly, it is possible to miniaturize an electronic device using the semiconductor device.
The related art semiconductor device 1 shown in FIG. 4, however, has an inconvenience that an outer size of the lower layer semiconductor element must be larger than an electrode area, in which electrodes are disposed, of the upper layer semiconductor element. The reason for this is as follows: namely, at the time of connecting the bonding wires to respective electrodes of the upper layer semiconductor element, some support is required to be disposed directly under each of the electrodes of the upper layer semiconductor element. If such a support is not provided (that is, in an overhang state), when the bonding wire is connected to each electrode of the upper layer semiconductor element, a mechanical load is partially applied to the upper layer semiconductor element, resulting in breakage of the upper layer semiconductor element.
The related art semiconductor device 25 shown in FIG. 5 has also an inconvenience that since the bonding wires must be connected to the lower layer semiconductor element, an outer size of the upper layer semiconductor element is required to be smaller than an electrode area, in which the electrodes are disposed, of the lower layer semiconductor element.
Accordingly, in each of the above-described related art semiconductor devices, there is a limitation to a relationship between the outer sizes of the lower layer semiconductor element and the upper layer semiconductor element. As a result, depending on a combination of outer sizes of semiconductor elements, the semiconductor devices cannot be stacked to each other, thereby failing to realize high density mounting of the semiconductor elements.